Interpretive Summary: Pea enation mosaic virus (PEMV) is a destructive virus of pea and other cool season legume crops. The virus has worldwide distribution but is not known to occur in New Zealand or Australia. New Zealand is an important winter seed increase nursery for USA pea seed companies. In 1978, a report was published in an obscure journal that PEMV was seed-transmitted in pea. However, no subsequent work has corroborated this observation. As a result of that report, regulations in New Zealand and Australia have prohibited the movement of pea seed from the USA without expensive time-consuming and laborious seed testing to certify that PEMV is not present. We collected a large sample of seed produced from plants infected with PEMV and evaluated the embryos, cotyledons, seed coat and the pod walls using the highly sensitive real-time reverse-transcription polymerase chain reaction to quantify the amounts of viral RNA in these seed tissues. Accumulation of PEMV RNA was significantly higher in pod walls and seed coats than in cotyledons or embryos. Although PEMV genomic RNAs were found in developing seed, no PEMV symptoms were observed in the field on more than 50,000 plants from seed derived from PEMV-infected source plants. These data demonstrate that PEMV is seed-borne in pea but do not support the previous report that PEMV is seed transmitted. Absence of seed transmission may result from the low abundance of PEMV viral genomes in embryo tissue. As a result of these findings, it is anticipated that required testing for PEMV in pea seed prior to exporting to New Zealand and Australia will be discontinued. This would reduce import and export restriction and help improve trade and reduce costs for the pea seed industry. In addition, winter increase of USA seed in New Zealand will allow for quicker introduction of improved cultivars into USA production.

Technical Abstract:
Pea enation mosaic virus (PEMV) is an important virus disease of pea. International movement of commercial pea cultivars and germplasm can be problematic due to uncertainty about seed transmission of the viruses responsible for the disease. Whether PEMV is seed-borne was assessed by collecting developing seed from infected plants and determining the relative concentrations of the PEMV-1 and PEMV-2 viral genomes using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). The relative accumulation of PEMV-1 and PEMV-2 was approximately 1,240 and 13,000 times higher, respectively, in leaf than in embryo tissues. Accumulation of PEMV-1 and PEMV-2 RNA was also significantly higher in pod walls and seed coats than in cotyledons or embryo axes. No evidence was obtained for seed transmission of PEMV in pea. Although PEMV-1 and PEMV-2 genomic RNAs were found in developing seed, no PEMV symptoms were observed in the field on more than 50,000 plants from seed derived from PEMV-infected source plants. These data demonstrate that PEMV is seed-borne in pea but do not support a previous report that PEMV is seed transmitted. Absence of seed transmission may result from the low abundance of PEMV viral genomes in embryo tissue.